This invention relates to a fuel injection control apparatus for use with an internal combustion engine operable on a gasoline/alcohol fuel blend and, more particularly, to such a fuel injection control apparatus for adjusting the time at which fuel injection is initiated to ensure that the fuel injection is terminated at a particular time.
For example, Japanese Patent Kokai No. 59-29733 discloses a fuel injection control apparatus which adjusts the time at which fuel injection from a particular fuel injector is initiated in a manner to ensure that the fuel injection is terminated at a particular time. The time at which fuel injection is terminated is set to a fixed crankshaft angular position near the beginning of the intake stroke of the corresponding piston in order to render the air-fuel ratio lean during transitional engine operation and obtain fuel economy during steady engine operation. The amount of fuel metered to the corresponding cylinder, this being determined by the duration of fuel injection from the particular fuel injector, is calculated based upon various conditions of the engine that are sensed during its operation. These sensed conditions include engine load, engine speed, cylinder-head coolant temperature, etc. The calculated duration of fuel injection is converted into the corresponding number of crankshaft degrees. The time at which the fuel injection is initiated is set to a crankshaft angular position by substrating the crankshaft angles from the crankshaft angular position at which fuel injection is terminated. Fuel injection from the particular fuel injector is initiated when the engine crankshaft reaches the angular position set for the time at which fuel injection is initiated. For this purpose, crankshaft position pulses each corresponding to two degrees of rotation of the engine crankshaft is counted after the engine crankshaft reaches a reference position provided for the particular cylinder.
In recent years, alcohol has been used in automotive vehicles either pure or blended with gasoline. The amount of fuel metered to the engine is controlled based upon the alcohol concentration of the fuel on which the engine is operating. The greater the percentage of the alcohol fuel contained in the gasoline/alcohol fuel blend, the smaller the stoichiometric air/fuel ratio and the greater the amount of gasoline/alcohol fuel blend that must be delivered to the engine to maintain the desired optimum air/fuel ratio. For example, when the gasoline/alcohol fuel blend has an alcohol concentration of 85 volumetric percentages, the required amount of gasoline/alcohol fuel blend is substantially twice the required amount of straight or 100% gasoline fuel for the same amount of air. If the time at which fuel injection is terminated is set to a crankshaft angular position, for example, near the beginning of the intake stroke of the piston, suitable for straight gasoline fuel, the time at which fuel injection is initiated will be set to a crankshaft angular position before the reference position, resulting in improper air/fuel metering control when the gasoline/alcohol fuel blend has a high alcohol concentrations. This is true particularly when the engine is operating at high-load and/or high-speed conditions. If the time at which fuel injection is terminated is set to a crankshaft angular position, for example, near the end of the intake stroke of the piston, suitable for gasoline/alcohol fuel blend having a high alcohol concentration, appropriate fuel combustion cannot be obtained when the engine is operating on gasoline/alcohol fuel blend having a low alcohol concentration.
This dilemma may be overcome by increasing the amount of fuel injected to the engine per unit time so as to decrease the required time interval of fuel injection. However, this requires the use of fuel injectors having a slow response time and a limited service life resulting from deposite problems when the fuel has a high alcohol concentration.